Despite persistent rumors that Sen. Mark Dayton (D-Minn.) could face a major primary challenge in 2006, no big-name Democrat to this point has come forward to take on the freshman Senator.

Three prominent Democrats whose names have been mentioned as possible challengers whole-heartedly threw their support behind Dayton in interviews with Roll Call last week, proving that most of the early action in the Gopher State Senate race will be in the Republican primary.

But two of the Democrats — former Rep. Bill Luther and lawyer Mike Ciresi, the runner-up to Dayton in the 2000 primary — refused to rule out running for higher office in the future.

Dayton is likely to be a top target of Republicans in 2006, and some Democrats in Washington, D.C., have quietly suggested that the party ought to search for a stronger potential nominee.

With his liberal voting record and controversial actions — including closing his Capitol Hill office in the weeks before Election Day for fear of a terrorist attack — Dayton is more vulnerable than most of the Democratic freshmen in 2006. But those facts have not been enough to entice a strong Democrat into the race against him.

“Mark Dayton is a good friend of mine,” said Luther, who lost his bid for a fifth House term in 2002. “I am not saying I would never run in the future [for political office] but I would never challenge Mark Dayton. He’s a close friend, and I’m a big supporter.”

Luther said his name was first circulated as a Senate candidate in a Robert Novak column, but insisted there was no truth to the rumor.

Ciresi, a wealthy Minneapolis lawyer who helped the state government win a huge settlement from the tobacco industry several years ago, said he would “absolutely, in a nanosecond” consider running for Senate in 2006 if Dayton decided to retire, but would not run against him, despite their ideological differences.

“I don’t think that would make any sense,” the centrist Democrat said. “If Mark’s going to run, we should all get behind him. It’s going to be a tough battle.”

Running in the 2000 Senate primary against the free-spending Dayton, the liberal heir to the Dayton’s retail chain, Ciresi spent more than $4 million of his own money but fell well short, taking 22 percent of the vote and finishing second. Dayton took 41 percent in the multiple-candidate contest.

Ciresi would not rule out running for governor in 2006, when Republican Tim Pawlenty is up for a second term, but he said it was not likely. He also would not rule out challenging Sen. Norm Coleman (R) in 2008, though he said it was too far in the future to think about seriously.

“That’d be fun just to do it,” Ciresi said. “Norm’s core value is Norm. He’d be a lot of fun to take on in a campaign.”

Meanwhile, some Democrats have turned longingly to Vance Opperman, a millionaire publisher from Eagan and big Democratic donor, and urged him to run. But the head of the Westlaw publishing empire demurred.

“I support Mark Dayton 100 percent,” he said. “I would never run against him.”

Opperman has also rejected suggestions that he run against Coleman in 2008.

“Norm’s an old friend, [and] I’d be much too old to do that,” he said.

Opperman said that while he considered running for the Senate in 2000, he can no longer imagine a scenario under which he’d run for any political office, because he is too busy enjoying watching his children grow up.

“The republic will do just fine if I’m not involved,” he declared.

Opperman suggested that the rumor mill of a strong primary challenge to Dayton is being churned by a number of factors.

“There are far extreme Republicans who would love for Mark Dayton to have lots of problems,” he said. Add “political boredom and mischief” to the recipe and voila, everyone is a potential candidate, he said.

Opperman predicted that Dayton will sail into the general election.

“Mark will be easily endorsed [by the party] and I’ll doubt that he’ll have any major competition of any kind,” he said.

Republicans are salivating at the possibility of taking Dayton down this cycle.

He has already said that he cannot spend the $12 million from his own pockets he expended in 2000 and that he is looking to the Democratic Senatorial Campaign Committee for help. Dayton had just $191,000 in his campaign account at the end of 2004.

Reps. Gil Gutknecht (R) and Mark Kennedy (R) are both considering a run, as is former Sen. Rod Grams (R), whom Dayton defeated to win the Senate seat in 2000.

Kennedy, who is seen as the early favorite of national Republican leaders, had just $66,000 in the bank Dec. 31 following a tougher-than-expected re-election race last year. Gutknecht had $361,000 on hand.

Former Rep. Vin Weber (R) has also been mentioned as a potential candidate. He did not return phone calls seeking comment on his possible interest in a Senate race.